White balance is not a natural concept for most of us. When we see an object, the light is collected by our eyes and sent to our brain, where it is processed, to produce an image. Over time we have learned that things are usually white, green or some other colour and when we see them, our brain will adjust the actual colour to what colour it "should" be.

However, our camera does not possess the ability to learn and if there is a colour cast, our camera will record it. Digital cameras are designed to do a certain amount of correcting automatically. That's good news for us and in most situations, we can use the auto white balance. Makes life simple.

It's easy make a mistake and I would suggest that if your camera can shoot in RAW mode, you should use this mode. The reason is that if you get your white balance wrong, when shooting, it's possible to correct it, most of the time in your camera RAW processor.

So, what difference does the white balance make. In the series of images below, I have in fact edited the same image four times but changed the white balance in each.

Each image was edited in exactly the same way as the others, except I changed the white balance. As you can see, I've indicated the white balance by printing it in the top left corner. The results are very different.

This shot was taken at about 2pm, so the Daylight white balance is the more accurate. The auto, in this case got it wrong and looks more like the Shade white balance.  At least 50% of the building walls are in shadow and the river is also dark. This may have fooled the camera into thinking the subject was in the shade. I don't know for sure.

This series of images shows how choosing the correct white balance can be critical. Imagine if you shot in auto at a wedding. The brilliant white wedding dress would come out as off white.

Had I not shot the image in RAW, I would not have been able to correct the white balance. 

You've seen the effect in daylight, at night it's even more critical, especially if there is more than one light source. All artificial light has a colour cast. In public buildings and retail outlets, the fluorescent lighting is usually daylight balanced. Fluorescent lighting in the home will have a purple or green cast, depending on which standard has been used in it's manufacture. Sometimes, it may have another colour.

Tungsten lighting is usually strongly yellow, the lower the wattage, the more yellow it is. Candles and fires also give off a yellow light. We know this already but our brains will clean up the colour cast caused by them.

When we see white, what is happening is that all of the light falling on the object is reflected back and enters our eyes. If there is no colour cast in the light(it's pure white), that will mean that the object is pure white but if the light falling on the object has a yellow cast, we should see the object as yellow.

Our brain can sort that out for us but our camera has to be told how to. So, that's why you would pick a white balance to match the lighting, especially in artificial light. If you have more than one source of light, of different colours, then you must decide which is the most important.

In the image below, taken in Limerick, during Christmas 2010, you will see that there are several light sources.

The street lights have a yellow cast, as you would expect. The top of the building on the right is flood light by a light with a blue cast but we would see it as white. The tree itself also has a blue cast but again we would have seen it as white and it was described as white by newspaper articles about it. To the left of the tree you will see a window with a greenish light inside. This is a domestic fluorescent light and the it too would have looked white to those in the room.

As you look further through the image, you will notice many windows with light inside, of several different colours. However, to the occupants, each of these lights would look white.

This image has been edited in exactly the same way as the one above, except I changed the white balance to Fluorescent. Looking now you will see the the light at the top of the building on the right is white. The light inside the window to the left of the tree is also white.

The street lights are a stronger yellow, as are the lights inside many of the windows. The tree is less blue.

Again nothing has been changed, except the white balance. The tree is now white, the street lights and yellow window lights are even more yellow and the light at the top of the right hand building has changed tone.

Which one is correct? It depends on which item in the image is most important. It was taken to show the tree and it's position in relation to the water front, so, for me, the last one is correct. It's set to Flash, even though I did not fire the flash but the lights in the tree and the flash are both daylight balanced. That is why it works.

If you were to stand where I took this shot from and looked at the river bank, you would not see the lighting as being as yellow as it is in the final image. In fact, if you had been in that light for a few minutes, you would not see it as yellow, at all.

So, that's it for now. As usual, feel free to ask questions or make comments, using the comments section below or by emailing me at [email protected] Suggestions for future blogs are also welcome.

Until next time, take good care of yourself and those you love.

Bye,
Eddie

So, now that you know the three factors that effect your exposure, lets see how to use them in practice.

The image above was taken at the Way of the Cross procession, in Newcastle West, on Good Friday last. It was a cloudy day and even though it seemed bright to the human eye, light levels were low. The default ISO rating for my camera is 200 but at that level I was getting shutter speeds too slow to hand hold and avoid camera shake.

I increased my ISO rating to 500. This means that at the same F number I can get shutter speeds that are 2.5 times what I would get at 200, 500 being 2.5 times 200. With experience, I have learned to hold the camera steady at relatively slow shutter speeds, for example 1/60th or 1/125th of a second. You may need to increase your ISO to 1000 or higher, depending on how steady a hand you have.

When choosing an ISO rating, remember that you should pick the lowest rating you can get away with, so as to reduce noise levels. While it can be fixed in Photoshop and most other editors, it is always better to get is as right in camera as possible.

Next I set the camera on Aperture Priority. This is usually denoted by A on your camera's selection dial. I've already selected the ISO rating and I will now select the aperture or F number. 

The camera will then automatically select the shutter speed. This doesn't mean that I can forget completely forget about my shutter speed, it's just the the camera does the math for me. I need to be aware of the shutter speed selected because if it's slow, my images will suffer from camera shake or motion blur, neither of which can be fixed.

It's always good to take a test shot, to see what speed is selected and then look at the enlarged image on your screen, to check for camera shake. If you have some, increase your ISO again and take another test shot. Only go up one step at a time, don't jump from ISO 400 to 1600, for example, try use the lowest rating you can.

During the procession, I checked my shutter speed each time the light looked to have faded. This happened when they came into narrower streets or were in the shadow of a building, for example. I also checked it regularly over time, as light fades as the afternoon passes, anyway. I maintained my shutter speed by increasing my ISO. By the end of the procession, I was using ISO 1600.

My next decision was which aperture or F number to use. This varied from photo to photo but for this one I used F11. The woman in the image was part of a group of three and I wanted to be sure that if any part of the others came into the image, they would be out of focus. As you can see, there is a large crowd(number not weight) in the background and I wanted them out of focus also.


To pick her out from the crowd I used a 70 - 300mm zoom lens at 270mm. 


If you look closely at the image, you will notice that she is sharp, except for her far shoulder. A shoulder and head from other people, on the left side of the image and the people in the background, on the right side, are all out of focus.


The result is that the lady herself, my subject, stands out, without competition from any other element of the image. Had I used a much smaller F number, say F4, only the point of focus and a little bit around it would have been sharp, most of the woman would be out of focus.


Had I used a much larger F number, say F22, most of the image would be in focus and she would have had to compete with the people in the background and the bits of people visible in the foreground, for attention. As a portrait, it would not have worked.


I focused on her eye. In most portraits, the person's eyes are the most important. If you have sharp eyes and other parts of the face are out of focus, the image still works. However, if the eyes are out of focus, it doesn't matter how sharp the rest of the image is, it wont work.